Priority is claimed to Korean Application No. 99-11267 filed on Mar. 31, 1999, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a cavity resonator for reducing the phase noise of electromagnetic waves output from a monolithic microwave integrated circuit (MMIC) voltage controlled oscillator (VCO) by utilizing a semiconductor (e.g., silicon, GaAs or InP) micro machining technique.
2. Description of the Related Art
Since a microwave/millimeter wave MMIC VCO, which does not use a cavity, outputs electromagnetic waves having large phase noise, the MMIC VCO is not appropriate for use in a radar system using a frequency modulating continuous wave (FMCW). Recently, dielectric disks or transmission lines have been utilized as resonators to reduce phase noise. However, dielectric resonators for millimeter waves are very expensive and are difficult to mass produce because the frequency at which resonance occurs depends on the location of the dielectric resonators and it is difficult to specify the location of the dielectric resonators in an MMIC substrate. Moreover, the Q-factor of transmission line resonators is too small to reduce phase noise.
FIGS. 1A and 1B are a plan view and a sectional view, respectively, of a conventional cavity resonator, and show a structure of an X-band micromachined resonator which is disclosed in IEEE Microwave and Guided Wave Letters, Vol. 7, pp. 168, 1997. The conventional cavity resonator is structured such that two microstrip lines 30 are coupled to a cavity 20 through two slots 10. Such a structure implements a transmission type resonator having an input port and an output port. Since the transmission type resonator has a more complicated feed structure than a reflection type resonator, it is difficult to design the transmission type resonator having a larger Q-factor.
To solve the above problems, it is an objective of the present invention to provide a cavity resonator for reducing the phase noise of electromagnetic waves output from a monolithic microwave integrated circuit (MMIC) voltage controlled oscillator (VCO) by coupling a silicon micromachined cavity, which has a large Q-factor, to a microstrip line such that the silicon micromachined cavity can be employed in a reflection type VCO.
Accordingly, to achieve the above objective, there is provided a cavity resonator for reducing the phase noise of a voltage controlled oscillator. The cavity resonator includes a cavity formed by a lower metal film and an upper ground plane metal film. The lower metal film is formed by etching a semiconductor into a six-sided or rectangular parallelepiped structure and depositing a conductive film on the six-sided or rectangular parallelepiped structure. The upper ground plane metal film is formed to cover the top of the rectangular parallelepiped structure of the lower metal film. A microstrip line of predetermined width is formed to extend from one end of the cavity across to the other end of the cavity to serve as a waveguide. The microstrip line is disposed a uniform predetermined distance from the upper ground plane metal film of the cavity. A slot is formed perpendicular to the microstrip line by removing a part, of predetermine dimension, of the upper ground plane metal film.
Preferably, the lower metal film, the upper ground metal film and the microstrip line are formed of a conductor selected from the group consisting of gold (Au), silver (Ag) and copper (Cu). The predetermined distance between the microstrip line and the upper ground metal film is maintained by interposing a substrate formed of a semiconductor or an insulating material between them.
In another aspect of the present invention, there is provided a cavity resonator for reducing the phase noise of a voltage controlled oscillator. The cavity resonator includes a cavity formed by a lower metal film and an upper ground metal film. The lower metal film is formed by etching a semiconductor into a rectangular parallelepiped structure and depositing a conductive film on the rectangular parallelepiped structure. The upper ground plane metal film is formed to cover the top of the rectangular parallelepiped structure of the lower metal film. A microstrip line of predetermined width is formed to expand across the cavity to serve as a waveguide. The microstrip line is disposed a uniform predetermined distance from the upper ground plane metal film. Two slots are formed parallel to the microstrip line by removing a part, of predetermine dimension, of the upper ground plane metal film. A matching resistor is inserted into the microstrip line at a predetermined location. The resistor is inserted into the microstrip line by removing a part, of predetermined width, of the microstrip line, at a location corresponding to one end of the cavity.
Preferably, the lower metal film, the upper ground metal film and the microstrip line are formed of a conductor selected from the group consisting of gold (Au), silver (Ag) and copper (Cu). The predetermined distance between the microstrip line and the upper ground metal film is maintained by interposing a substrate formed of a semiconductor or an insulating material between them.